Cathode ray oscilloscopes



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LAWLOR CATHODE RAY OSCILLOSCOPES Feb. 17, 1959 Filed Dec. 1, 1952INVENTO&

F61 17, 1959 R, c, LAWLQR 2,874,377

, CATHODE RAY OSCILLOSCOPES Filed Dec. 1, 1952 I :s Sheets-Sheet 2fifiglan 44a IN TENS TY IN V EN TOR.

Feb. 17, 1959 R. c, LAWLOR 2,874,377

w CATHODE RAY OSCILLOSCOPES Filed Dec. 1. 1952 3 Sheets-Sheet 3 no 050INVENTOR.

United States Patent Ofice i 2,874,377 Patented Feb. 17, 1959 z,s14,s17

csrnonr: RAY OSCILLOSCOPES Reed 0. Lawlor, Alhambra, cnu.

Application December I, 1952, Serial No. 323,395 I as Claims (Cl.340-369) This invention relates to improvements in cathode ray tubes andparticularly to improvements for enhancing the contrast of images formedon the screens of such tubes.

Cathode ray oscilloscopes and similar devices have been developed forgenerating and erasing images formed on a phosphorescent or otherimage-retentive screen. Such a system is disclosed and claimed in myco-pending patent application, Serial No. 619,347, filed October 30,1956, which application is a continuationin-part of a prior application,Serial No. 558,165, filed October 11, 1944, now abandoned, which in turnwas a continuation-in-part of my patent application, Serial No. 365,981,filed November 16, 1940, now Patent No. 2,363,600. In such systems,images that are formed by bombardment of the screen with acceleratedelectrons or otherwise are periodically erased by flooding the screenwith suitable radiation such as infra-red radiation. In some cathode rayOscilloscopes, the persistence of the image 'is varied by controllingthe amount of a certain type of radiation, such as infra-red radiation,falling upon the screen while the image is being formed. Both in thecathode ray tubes employed in the aforementioned oscilloscopes and inmany other cathode ray tubes, luminescent screens are employed which areaffected by short wavelength radiation and by'long wavelength radiation.In both arrangements the contrast in the-image is affected adversely bysuch radiation from external sources.

One of the objects of the present invention is to provide a cathode raytube with a filter for increasing image contrast by preventing anyundesired external radiation from reaching the image which would reducethe sensitivity of luminescent screen, erase images formed thereon, orexcite the screen.

Another obejct of this invention is to provide a cathode raytube inwhich deexciting energy is prevented from reaching the screen from thefront side thereof.

Another object of this invention is to provide a cathode .ray tube inwhich exciting energy is prevented from reaching the screen from thefront side thereof.

Another object of this invention is to improve the contrast of imagesproduced by a cathode ray tube by preventing extraneous radiation fromaffecting the screen unnecessarily and that will at the same timeprevent visible radiation from reaching the screen from the front of thetube and then being reflected to an observer at the front of the tube.

Still another object of my invention is to provide a cathode ray tubeemploying a cascade screen having a reflecting backing that reflectsradiation employed to excite the screen but which is transparenttodeexciting energy projected toward the screen from a point behind thescreen. v

The foregoing and other objects of the invention will he more readilyapparent from a consideration of the various embodiments of theinvention illustrated in the accompanying drawings and describedhereinbelow.

by the cathode rays impinging In the drawings wherein like referencecharacters indicate like elements throughout the several views:

Figure l is a longitudinal cross-sectional view of a Fig. 5 is afragmentary cross-sectional view of a cascade screen to which theinvention is applied;

Fig. 6 is a fragmentary side elevation of an alternate embodiment of theinvention with some of the parts shown in cross-section;

Fig. 7 is a fragmentary cross-sectional view of'an al ternate embodimentof the invention;

Fig. 8 is aside elevation of an alternative embodiment of the invention;

Fig. 9 is a graph of radiation intensity versus time employed inexplaining various forms of the invention; and

Figs. 10, 11, 12 and 13 are graphs representing the spectralcharacteristics of various parts employed in the invention. 7

In one embodiment of the invention illustrated in Figs. 1 to 4 of thedrawings, a cathode ray tube 10 is provided with a luminescent screen12, a source of erasing radiation 14 behind the screen, and a filterstructure 16 in front of the screen. The screen 12 is composed of aphosphorescent material which becomes visibly excited thereon. Thecathode ray tube 10 is mounted with its forward end inserted within afelt-lined mounting cylinder 17 supported upon a panel 19 of aninstrument case, thus positioning the screenlZ where it is readily seenby an observer. The filter 16 is mounted in the cylinder 17 between thescreen 12 and the observer. The luminescent screen 12 is of a type inwhich visible images are formed thereon by bombardment with cathodesays. For example, the

, images may be of the oscillograph trace type in which a beam is causedto scan the screen. under the influence of sweep voltages and signalvoltages. or the images may be of. the variable intensity or variablearea type produced by modulating the cathode ray beam as it scans thescreen 12, in a predetermined pattern.

The image formed by the impinging cathode rays causes the luminescentscreen to phosphoresce visibly for a prolonged period, the length ofwhich depends upon the persistence that characterizes the particularscreen material of which the screen is composed. In this embodiment ofthe invention, the screen is also characterized by becoming visiblyexcited by short wavelength electromagnetic radiation, such as violetrays or long wavelength ultra-violet rays. The relative intensity ofradiation emitted when the screen is excited by a given strength ofradiation of different wavelengths is indicated by graph X of theexcitation spectrum shown in Fig. 10. The relative intensity ofradiation emitted at different wavelengths when the screen is' excitedeither by cathode rays or short wavelength radiation is indicated by thegraph M of the emission spectrum in Fig. l0. When once excited, thescreen continues toemit such radiation for a prolonged period. Thisscreen 12 is also characterized by becoming deexcited upon exposure toelectromagnetic radiation ina range of relatively long wavelengths, suchas orange or infra-red radiation. Either the intensity of the imageformed on the screen may be decreased more rapidly than otherwise or itmay be momentarily increased and then decreased. The relative etficiencywith which radiation known and include many of the-zinc sulphidephosphors,

not? including those that contain small portions of copper, togetherwith minute quantities of other impurities.

The deexcitation characteristics of luminescent materials-of thetypesmentioned above may be understood by reference to Fig. 9. In thisfigure, the intensity of the image formed at any point of thescreen isplotted as a function of time. When a beam of cathode rays of uniformintensity strike the screen for a time interval T the intensity. ofluminescence increases rapidly, along-v curve a, asymptoticallyapproaching a saturation value 8. When the cathode ray beam is turned oris directed toward some otherpart of the screen, the intensity of theradiation emitted from the excited area decays along the curve b at arate depending upon the exact conditions of the excitation by thecathode ray beam and also dependent upon the characteristics of theparticular matesource 14 is nergized, while the dash portion b" of curve1: indicates ow the intensity would continue to diminish if theradiation source 14 were to remain-unenergized.

However, when the radiation source-14 (see Fig. 1) is energized for aperiod T,, the intensity of the image decreases rapidly along the heavycurve e for certain types of materials and then after the source 14 isdeenergized. continues to diminish along the light curve 0''. with thistype of material the intensity on the image is less after exposure toradiation from the source 14 than .it otherwise would be if that sourcehad remained -'unenergized.

I With other types of materials, the intensity of the image is enhancedfor a limited time when exposed to radiation from the source 14 and thendecays rapidly, as indicated by the curve d. After the source 14 isdeenergized the intensity continues to decay along the curve d,eventually becoming less than the intensity would otherwise be if thesource 14 had not been energized. It is interesting to note that if thetime interval T, for which the source 14 is energized-is relativelyshort, then after deenergization the intensity of the image may begreater than it would have been in the absence of radiation from thesource 14, as indicated by the portion of the curve 4 above the curve b.However, if the source 14 remains energized sufficiently long, theintensity of the image may be brought to a level below that of sectionb" of the curve b before the source 14 is deenergized.

In either event, whether curves c and c" or curve d is followed, thescreen becomes deexcited by exposure to radiation from the source 14 andthe image previously produced thereon by the cathode rays is erased.

October 11, 1944, now abandoned, there are described arrangements forforming and erasing images. According to the present invention, thecontrast of theimages so formed is increased by employment of a filter16. As indicated in Fig. 2, this filter consists oftwo parts or layers18 and 20. These two filter elements 18 and 20 may be cemented togetheror may be separated by an air space, depending upon the characteristicsof the particular materials employed.

One of these filter elements 18 is in the form of a filter whichtransmits visible radiation from the image formed Thus,

- rection to the screen from being transmitted'thcrethrough theexcitation effects that would otherwise .be produced by such shortwavelength radiation reaching the screen from the front, are eliminated.

The "filter element 18 may be of one of two types. Either it may consistof an ordinary optical filter which transmits radiation in a part of thevisible range and absorbs long wavelength radiation includi g infra-red60 In copending application Serial No. 558,165, filed a 4 radiation andalso absorbs short wavelength radiation inin the visible range and toabsorb or reflect radiation in the ultra-violet and infra-red regions.Characteristics of suitable filters are indicated in Fig. 11 where Trepresents the transmission spectrum and U and I represent thereflection or absorption spectra in the short and long wavelengthregions respectively. If a semi-transparent layer of gold is employedfor this purpose, it absorbs short wavelength radiation such asultra-violet, transmits visible radiation such as the green, andreflects long wavelength radiation such as the long red and infra-red.In any event, in accordance with this invention, infra-red radiation andultra-violet radiation from the space in front of the screen areprevented from reaching the screen while visible radiation from theimage is readily seen through the filter 16. The image so producedpossesses more contrast than the image that would be seen in the absenceof the filter element 18.

The second filter element 20 may be an optical rectifier, that is, itmay consist of a material which permits radiation to travel in onedirection therethrough from in front of the screen but which preventsradiation which travels therethrough to the screen from beingtransmitted therethrough in the opposite direction after.

regular reflection from the screen 12. Optical rectiflers of that typeare sold under the trademark Polaroid" and are manufactured by the LandCorporation. These rectifiers employ certain principles of polarizedlight to adapt them to prevent light that is transmitted in one diin theposite direction after regular reflection from the screen. ith thisarrangement, visible light from a point in front of the screen 12 ishighly attenuated, thus minimizing interference. with the image that isundergoing observation and thus enhancing the contrast of the imagebeing viewed.

While this invention is applicable to any cathode ray tube employingluminescent screens which are excited by relatively short wavelengthradiation and deexcited by relatively long wavelength radiation, it isparticularly applicable to systems such as those described in myaforementioned copending patent applications, which utilize suchlongwavelength radiation to erase images or to control their persistence.

- As indicated in Fig. l, the cathode ray tube of the present embodimentof the invention has a cylindrical head 30 having a face 31 forming abase for the screen 12. The cylindrical head 30 is connected at the rearend thereof by a step 32 to a conical neck 33, connected to acylindrical shank or leg 34. A terminal connector 35 is mounted at therear end of the shank 34 opposite the screen. Mounted within the shank34 and suitably connected to the connector 35 is a source of cathoderays. In addition, electrostatic deflecting plates may be mounted inthat shank or magnetic deflecting coils may be mounted around the shank.In either case, the defleeting plates or coils are employed to cause abeam of accelerated electrons, that is, cathode rays, to scan the screen12 in whatever manner is desired to. produce an image thereon. ,jg;

A first ring 40 of conductive material is'co'a ted onthe interior of thecylindrical portion andv another ring 41 of conductive material iscoatedon the interior oi the conical portion 33,- the two rings beinginterconnected by .narrowstrips 42 of such conductive material coatedalong the interior of the step 32, thus providing a highly transparentwindow in the step, that is, a window in which the open space is muchlarger than the intervening opaque spaces formed by the strips. The tworings 40 and 41 of conductive material form an electrostatic Shield forthebeam directed to the screen 12.

' regions.

a plurality of rearwardly extending resilient fingers 46 that are curvedinwardly at their rear ends as shown in Figs. 1 and 4. The clamping ring44 is preferably coated with felt or other shock-absorbent material onthe inner side thereof, both in the solid ring portion and in the fingerportions to minimize shock. The radiation source 14 is also providedwith two rearwardly directedlegs 48 in which the electrical leads aremounted as shown in Fig. 3..

The radiation source 14 may be of many different forms. For example, ifinfra-red radiation is being employed for era'singor for control ofpersistence, the tubular wall of the source may consist of glass whichtransmits infra-red radiation but absorbs visible and ultravioletradiation. The transmission and absorption spectra of such a materialare represented by the curves A and B respectively of Fig. 12. In anyevent, for maximum efficiency, the rear side of the source 14 is coatedwith a layer 50 of silver or other material that is highly refiective inthe infra-red region.

The radiation source 14 may be in the form of an incandescent lamp or inthe form of a gaseous discharge lamp. The employment of a circularsource is particularly advantageous because the magnetic fields producedby current flowing through the lamp have very small or negligiblecomponents transverse to the cathode ray beam that scans the screen 12.

In order to produce images of long'persistence, it is sometimesdesirable fo employ a cascade screen, that is,

a screen 12 comprising two or more layers 12a and 12b '.tion in apredetermined wavelength range such as in the visible range. A materialhaving the characteristics of the phosphor previously described inconnection with Fig. 10 is suitable for the front layer. The employmentof cascade screens is particularly desirable because images formed withphosphorescent materials generally persist longer when excited byultraviolet or other electromagnetic radiation than ode rays.

In another embodiment of the invention illustrated in Fig. 6, the frontfilter is incorporated in the face of the cathode ray tube. Thus, forexample, a filter element 18a having the characteristics of the filterelement 18 described above is mounted on the face of the tube and theluminescent screen 12c is deposited directly thereon. In this case, afront filter element in the form of an optical rectifier 20b asdescribed above is also mounted at the front of the tube either secureddirectly on the filter element 18a or spaced therefrom. Again cascadescreens are most suitable where long persistence is desired.

when excited directly by cathmama With this arrangement, infra-redradiation entering the screen from the source 14 is reflected rearwardlyby the dichroic surface, thus enhancing any deexciting effects. At thesame time, however, any infra-red radiation striking the cathode raytube from the front is reflected outwardly by the coating 61, preventingsuch radiation from erasing'or inhibiting phosphorescent images. Alsowith thisarrangemcnt, any ultra-violet radiation produced by the cathoderays striking the rear coating of the cascade screen is refiected-by-therear coating 63 and the dichroic coating 61 back into the screen, thusenhancing the effect of this radiation and increasing the excitation ofthe front arrangement, the dichroic coating 61 prevents extraneousultra-violet radiation from reaching the luminescent screen from thefront of the cathode ray tube. It is thusapparent that with thisarrangement, high intensity, high contrast images are produced free ofundesired background luminescence excited by external short wavelengthradiation and free of undesirable deexcitation from external sources.The contrast may be further enhanced by employing an optical rectifier20b on the outer side of the front face 31, as illustrated in Fig. 7a.

In Fig. 8 there is illustrated another form of the invention. This formof the invention is similar to the foregoing employing a cathode raytube comprising a cylindrical head 30b, a conical step 32b, a conicalneck 33b and a shank 34b attached to a connector 35b, and a tube face31b. A filter 16b is also mounted in front of the tube. In this case,however, the screen 12d is composed of a material which at normaltemperatures and under normal ambient conditions emits radiation very InFig. 7 there is illustrated a portion of another form r of cathode raytubeemploying this invention. In this case, the front face 31. of thetube is provided with a dichroie coating 61 on the interior thereof, anda cascade luminescent. screen 62 and a reflective rear coating 63 aredep titedfin the order named on the interior thereof. The dichroiecoating 61 is adapted to reflect radiation in the infra-redr'ange' andinthe ultra-violet range, but to transmit radiation in the visiblerange.The rear coating 63 is adapted tq'retlect'radiation in the visible andultraviolet ranges but to transmit radiation in theinfra-red Theluminescent screen 62 is of the cascade type described above.

slowly, if at all, even through a latent image is formed thereon bycathode ray beam excitation. With such a screen, after an image isformed, it is excited by suitable radiation, say infra-red radiation, todeexcite-the screen, thus causing radiation in-the visible range to beemitted, so that the image may be observed. Subsequently, when desired,the deexcitation may be accelerated by radiation in another range, suchas orange light, effectively erasing the latent image.

In this embodiment of the invention two tubular radiant energy sources14a and 14bare employed of the types hereinbefore described, both beingmounted behind a the luminescent screen. One of the sources 14a emitsinfra-red radiation and the other source 14b emits orange radiation,both being of annular tubular configuration and being mounted behind thescreen by means of a clamping ring 44a and compound fingers 46a. In thiscathode ray tube the screen 12c may also be of the cascade type andfilters of the type hereinbefore described may be employed.

Though the invention has been described hereinabove with reference tothe employment of a source 14 of radiation for erasing images formedthereon, it is useful in other ways. For example, the combination ofscreens and filters described are applicable where the source 14 ofradiation is energized continuously in order to control the persistencecharacteristic of the screen. Furthermore, it will be clear that many ofthe features of the combinations of filters and luminescent screen maybe applied in ordinary cathode ray Oscilloscopes in which no such source14 is present. For example, if the luminescent screen is composed ofmaterial which emits visible radiation when excited bycathode rays or byultra-violet rays and which is deexcited by infra-red few forms of theinvention have been specifically def scribed, the invention is notlimited thereto but is capable of a wide variety of mechanicalembodiments. Various changes which will now suggest themselves to thoseskilled in the art may therefore be made in the material, form, detailsof construction and arrangement of the various elements, withoutdeparting from the invention. In particular, it is to be understood thatthe luminescent screens, filters and coatings need not have all of thecharacteristics described, but that materials having some: of thecharacteristics described may be combined in accordance with the presentinvention in order to increase the contrast of images produced withcathode ray tubes. Reference is therefore to be had to the appendedclaims to ascertain the scope of the invention.

The invention claimed is:

1. In a cathode ray tube, a luminescent screen characterized by emittingradiation in a first wavelength region when excited either by cathoderays or by radiation in a second wavelength region and by becomingdeexcited upon exposure to radiation in a third wavelength region,

' said screen; afilter in front of said screen characterized byselectively attenuating transmission of radiation ,of such shortwavelengthsand such long wavelengths and also characterized byselectively transmitting radiation in said first wavelength region, anda separate source for emitting radiation in said relatively longwavelength region mountedbehind said screen.

- 2; In a' cathode ray tube, a luminescent screen characterized byemitting radiation in a first wavelength region when excited by cathoderays and by becoming deexcited upon exposure to radiation in a secondwavelength region, wavelengths in said second wavelength region beinglong compared with wavelengths in said first wavelength region; a sourceof cathode rays for exciting said screen; a filter in front of saidscreen characterized by'selectively attenuating transmission orradiation of such long wavelengths and also characterized by selectivelytransmitting radiation in said first wavelength region; and aseparatesource for emitting radiation in said long wavelength regionmounted behind said screen.

3. In a cathode ray tube, a luminescent screen characterized by emittingradiation in a first wavelength region when excited by cathode rays andby becoming deexcited upon exposure to radiation in a second wavelengthregion, wavelengths in said second wavelength region being long comparedwith wavelengths in said first rectifier in front of said screen forpreventing radiation in said first region that is transmittedtherethrough to said screen from being transmitted therethrough in theopposite direction after reflection from said screen; and a separatesource for emitting radiation in said second wavelength region mountedbehind said screen.

4. In a cathode ray tube, a luminescent screen characterized by emittingradiation in a first wavelength region when excited by cathode rays andby becoming deexcited upon exposure to radiation in a second wavelengthregion,

a wavelengths in said second wavelength region being long compared withwavelengths in said first wavelength region; a source of cathode raysfor exciting said screen; a reflecting coating behind said screencharacterized by selectively reflecting radiation in said firstwavelength region and also characterized by selectively transmittingradiation in said second wavelength region; and a separate source foremitting r adiation in said second wavev length region mounted behindsaid screen.

5. In a cathode ray tube, a luminescent screen characterized by emittingradiation in a first wavelength region when excited bycathode rays andby becoming deex-.

cited upon exposure to radiation in a second wavelength region,wavelengths in said second wavelength region being long compared withwavelengths in said first wavelength region; a source of cathode raysfor exciting said screen; a filter in front of said screen-characterizedby selectively attenuating transmission of radiation of such longwavelengths and also characterized by selectively transmitting radiationin said first wavelength region; a reflecting. coating behind saidscreen characterized by selectively reflecting radiation in said firstwavelength region'and also characterized by selectively transmittingradiation in'said second wavelength region; and a separate source foremitting radiation in said second wavelength region mounted behind saidscreen.

6. In a cathode ray tube, a transparent plate, a luminescent screen onthe rear side of said plate and characterized by emitting radiation in afirst wavelength region when excited by cathode rays and by becomingdeexcited upon exposure to radiation in a second wavelength region,wavelengths in said second wavelength region being long compared withwavelengths in said first wavelength region; a source of cathode raysfor exciting said screen; a filter in front of said screen characterizedby selectively attenuating' transmission of radiation of such longwavelengths and also characterized by. selectively transmittingradiation in said first wavelength region; an optical rectifier in frontof said screen for preventing radiation in said predetermined regionthatis transmitted therethrough to said screen from being transmittedtherethrough in the opposite direction after reflection from saidscreen; and a separate source for emitting radiation in said secondwavelength region mounted behind said screen.

7. In a cathode ray tube, a cascade screen comprising a front layer anda back layer, said front layer being characterized by emitting radiationin a first wavelength region when excited by radiation in a secondwavelength region and by becoming deexcited upon exposure to radiationin a third wavelength region, wavelengths in said second region beingshort compared with wavelengths in said first region and wavelengths insaid third region being long compared with wavelengths in said firstregion, said back layer being characterized by emitting radiation insaid second wavelength region when excited by cathode rays; a reflectingcoating behind said screen characterized by selectively reflectingradiation in said first wavelength region and said radiation in saidsecond wavelength regionand also characterized by selectivelytransmitting radiation in said third wavelength region; a source ofcathode rays for exciting said screen; and a separate source foremitting radiation in said third wavelength region mounted behind saidscreen.

8. In a cathode ray tube, a cascade screen comprising a front layer anda back layer, said front layer being characterized by emitting radiationin a, first wavelength region when excited by radiation in a secondwavelength region and by becoming deexcited. upon exposure to radiationin a third wavelength region, wavelengths in said second region beingshort compared with wavelengths in said first region and wavelengths insaid third region being long compared with wavelengths in said firstregion. said back layer being characterized by emitting radiation insaid second wavelength region when excited by cathode rays; a source ofcathode rays for exciting said screen;

a filter in front of said screen characterizedby selectively attenuatingtransmission of radiation of such short wavelengths and'such longwavelengths and also characterized by selectively transmitting radiationin said first wavelength region; a reflecting coating behind said screencharacterized by selectively reflecting radiation in said firstwavelength region and said radiation in said second wavelength regionand also characterized by selectively transmitting radiatiqn in saidthird wavelength region;

and a separate source for emitting radiation in said third wavelengthregion mounted behind said screen.

9. In a cathode ray tube, a cascade screen comprising a front layer anda back layer, said front layer being characterized by emitting radiationin a first wavelength region when excited by radiation in a secondwavelength a dichroic mirror in front of said screen characterizedbyselectively transmitting radiation in said first wavelength range andselectively reflecting radiation in said other wavelength regions; areflecting coating behind said screen characterizedby selectivelyreflecting radiation in said first wavelength region and said radiationin said second wavelength region and also characterized by selectivelytransmitting radiation in said third wavelength region; and a separatesource for emitting radiation in said third wavelength region mountedbehind said screen.

10. Ina cathode ray tube, a transparent plate,- a cascade screen on therear side of said plate and comprising a front layer and a back layer,said front layer being characterized by emitting radiation in a firstwave-length region when excited by radiation in a second wavelengthregion and by becoming deexcited upon exposure to radiation in a thirdwavelength region, wavelengths in .said second region being shortcompared with wavelengths in said first region and wavelengths in saidthird region being long compared with wavelengths in saidfirst region,said back layer being characterized by emitting radiation in said secondwavelength region when excited by cathode rays; a source of cathode raysfor exciting said screen; a filter in front of said screen characterizedby selectively attenuating transmission of radiation of such shortwavelengths and such long wavelengths and also characterized byselectively transmitting radiation in said first wavelength region; anoptical rectifier-in front of said screen for preventing radiation insaid first wavelength region that is transmitted therethrough to saidscreen from being transmitted therethrough in the opposite directionafter reflection from said screen; and a separate source for emittingradiation in said third wavelength region mounted behind said screen.

insaid first wavelength region that is transmitted therethrough to saidscreen from being transmitted therethrough in the opposite directionafter reflection from said screen; a reflecting coating behind saidscreen characterized by selectively reflecting radiation in said firstwavelength region'and' said radiation in said second wavelength regionand also characterized by selectively transmitting radiation in saidthird wavelength region; and a separate source for emitting radiation insaid third wavelength region mounted behind said screen.

12. In a cathode ray tube, a screen of luminescent material thereoncharacterized by emitting radiation in a first wavelength region whenexcited either by cathode rays or by radiation ina second wavelengthregion and by becoming deexcited upon exposure to radiation in a thirdwavelength region; wavelengths in said second region being shortcompared with wavelengths in said first region and wavelengths in saidthird region being long compared with wavelengths in said first regionand a dichroic mirror in front of said screen characterized bytransmitting radiation in said first wavelength region and reflectingradiation in said other wavelength regions.

13. In a cathode ray tube, a screen of luminescent material thereoncharacterized by emitting radiation in a first wavelength region whenexcited either by cathode Y raw or by radiation in a-second wavelengthregion and by becoming deexcited upon exposure to radiation in a thirdwavelength region, wavelengths in said second region being shortcompared with wavelengths in said first region and wavelengths in saidthird region being long compared with wavelengths in said first region;a dichroic mirror in front of said screen characterized by transmittingradiation in said first wavelength region and reflecting radiation insaid other wavelength regions; and a reflecting layer behind saidluminescent screen characterized byreflecting radiation in said firstwavelength region and radiation in said second wavelength region and bytransmitting radiation in said third wavelength region.

14. In a cathode ray tube, a screen of luminescent material thereoncharacterized by emitting radiation in a first wavelength region whenexcited by cathode rays and by becoming deexcited upon exposure toradiation in a second wavelength region, wavelengths in said secondwavelength 'region being long compared with wavelengths in said firstwavelength region, a dichroic mirror in front of said screencharacterized by transmitting radiation in said first wavelength regionand reflecting radiation in said second wavelength region, and areflecting coating behind said screen characterized by reflectingradiation in said first wavelength region and by transmitting radiationin said second wavelength region.

15. In a cathode ray tube, a screen of luminescent material thereoncharacterized by emitting radiation in a first wavelength region whenexcited by cathode rays and by becoming deexcited upon exposure toradiation in a second wavelength region, wavelengths in said secondwavelength region being long compared with wavelengths in said firstwavelength region, and a transmitting radiation in said first wavelengthregion region being long compared with wavelengths in said I rectifierin .front of said screen. for preventing. radiation and reflectingradiation in. said. secondwavelength region. g t

16. In a cathode ray tube, a luminescent screen, said screen comprisinga front luminescent layer and a back luminescent layer acterized bycmitti radiation in a first wavelength region when excited b radiationin a second wavelength region and by becoming deexcited upon exposure toradiation in a third wavelength region, wavelengths in -saidsecondregion being short compared with wavesaid first region, said backlayer,, being characterized sligereon, said front layer being charationin said other wavelength regions, and a reflecting coating behind saidscreen characterized by reflecting radiation in said first wavelengthregion and radiation in said second wavelength region and bytransmitting radiation in said third wavelength region.

17. In a cathode ray tube, a luminescent screen, said screen comprisinga front luminescent layer and a back luminescent layer thereon, saidfront layer being characterized by emitting radiation in a firstwavelength region when excited by radiation in a second wavelengthregion, said back layer being characterized by emitting radiation insaid second wavelength region when excited by cathode rays, wavelengthsin said second wavelength region being short compared with wavelengthsin said first wavelength region, a dichroic mirror in front of saidscreen characterized by transmitting radiation in said first wavelengthregion and reflecting radiation in said second wavelength region, and areflecting coating behind said screen characterized by reflectingradiation in said first wavelength region and radiation in said secondwavelength region.

18. in a cathode ray tube screen, a transparent plate, a luminescentscreen parallel to said plate and charactcrizcd by emitting radiation ina first wavelength region when excited either by cathode rays or byradiation in a second wavelength region and by becoming deexcited uponexposure to radiation in a third wavelength region. wavelengths in saidsecond region being short compared with wavelengths in said first regionand wavelengths in said third region being long compared withwavelengths in said first region, and a filter on the same side of saidscreen as said transparent plate characterized .by transmittingradiation in said first wavelength region therethrough and preventingradiation in said other wavelength regions from being transmittedtherethrough.

19. In a cathode ray tube screen, a transparent plate, a luminescentscreen parallel to said plate and charac' terized by omitting radiationin a first wavelength region when excited by cathode rays and bybecoming dccxcited upon exposure to radiation in a second wavelengthregion, wavelengths in said second wavelength region being long comparedwith wavelengths in said first wavelength region, and a filter on thesame side of saidscreen as said transparent plate characterized bytransmitting radiation in said first wavelength region therethrough andpreventing radiation in said second wavelength region from beingtransmitted therethrough. I

20. A filterfor a cathode ray tube employing a luminescent screen on therear side of a transparent plate and characterized by emitting radiationin a first wavelength region when excited by cathode rays or byradiation in a'second wavelength region and by becoming deexcited uponexposure to radiation in a third wavelength region, wavelengths in saidsecond region being short compared with wavelengths in said first regionand wavelengths in said third region being long compared withwavelengths insaid first region, said filter comprising a first filterelement characterized by transmitting radiation in said first wavelengthregion but also characterized by preventing transmission of radiation insaid second wavelength region and in said third wavelength region, and asecond filter element comprising an optical rectifier characterized bytransmitting radi ation therethrough in one direction from a source onone side thereof but not in said direction after being transmittedtherethrough in the opposite direction and then being regularlyreflected from a surface n the same side thereof as such source.

12 21. A filter for a cathode ray tube employing -a luminescent screenon the rear side of a transparent plate and characterized by emittingradiation in a first wavelength region when excited by cathode rays orby radiation in a second wavelength region, wavelengths in said secondwavelength region being short compared with wavelengths in said firstwavelength region, said filter comprising a first filter elementcharacterized by transmitting radiation in said first wavelength regionbut also characterized by preventing transmission of radiation in saidsecond wavelength region, and a second filter element com prising anoptical rectifier characterized by transmitting radiation therethroughin one direction from a source on one side thereof but not in saiddirection after being transmitted therethrough in the opposite directionand then being regularly reflected from a surface on the same side assuch source.

22. A filter for a cathode ray tube employing a luminescent screen onthe rear side of a transparent plate and characterized by emittingradiation in a first wavelength region when excited by cathode rays andby becoming deexcited upon exposure to radiation in a second wavelengthregion, wavelengths in said second wavelength region being long comparedwith wavelengths in said first wavelength region, saidfilter comprisinga first filter element characterized by transmitting radiation in saidfirst wave length region but also characterized by preventingtransmission of radiation in said second wavelength region, and a secondfilter element comprising an optical rectifier characterized bytransmitting radiation therethrough in one directionfrom a source on oneside thereof but not in said direction after being transmittedtherethrough in the opposite direction and then being regularlyreflected from a surface on the same side thereof as such source.

23. In a cathode ray tube, a luminescent screen having a characteristicthat is altered in a first wavelength region when excited by cathoderays and that is restored upon exposure to radiation in a secondwavelength region; a source of cathode rays for exciting said screen; afilter in front of said screen characterized by selectively attenuatingtransmission of radiation in said second wavelength region and alsocharacterized by selectively transmitting radiation in said firstwavelength region whereby altered areas may be distinguished fromunaltered areas by viewing said screen through said filter; and aseparate source for emitting radiation in said second wavelength regionmounted behind said screen.

24. In a cathode ray tube, a luminescent screen having a characteristicthat is altered in a first wavelength region when excited by cathoderays and that is restored upon exposure to radiation in a secondwavelength region, wavelengths in said second wavelength region beinglong compared with wavelengths in said first wavelength region; a sourceof cathode rays for exciting said screen; a filter in front of saidscreen characterized by selectively attenuating transmission ofradiation of such long wave lengths and also characterized byselectively transmitting radiation in said first wavelength regionwhereby altered areas may be distinguished from unaltered areas byviewing said screen through said filter; and a separate source foremitting radiation of such long wavelengths mounted behind said screen.

25. In a cathode ray tube having an envelope, a luminescent screenmounted within said envelope adjacent one end of said envelope, thematerial forming said screen having a characteristic that is altered ina first wavelength region when excited by cathode raysand that isrestored upon exposure to radiation in a second wavelength region, saidend of said envelope being transparent in said first wavelength regionwhereby alterations in the screen in said first wavelength region areobservable through said end of said envelope; means including a sourceof cathode rays mounted within said envelope for directing a beam ofcathode rays at said screen and for causing said beam to scan saidscreen; and a source for emitting radiation 13 in said second wavelengthscreen and said cathode ray'source.

26. In a cathode ray tube, a tubular envelopehaving an enlarged faceatone end and a small neck at the other end; a luminescent screenmounted within said envelope adjacent said,face,.the material composingsaid screen having a characteristic that is altered in a firstwavelength" region .when excited-by cathode rays and that is restoredupon exposure toradiation in a second wavelength region, said end ofsaid envelope being transparent in said first wavelength region wherebyalterations in the screen in region mounted between in said secondwavelength region encircling said tubular member behind said step.

.connected to said shank by a conical neck and a step,

said first wavelength region are observable through said end of saidenvelope; means including a source of cathode rays mounted within saidneck for directing a beam of cathode rays at said screen and for causingsaid beam to scan said screemand a source for emitting radiation in'saidsecond wavelength region encircling the axis of said tubular envelopebetween said screen and said cathode.ray source.

27. In a cathode ray tube comprising a tubular envelope, a luminescentscreen mounted within said envelope at one end thereof, the materialcomposing said screen having a characteristic that is altered in a firstwavelength region when excited by cathode rays and that is restored uponexposure to radiation in a second wavelength region, said end of saidenvelope being transparent in said first wavelength regionwherebyalterations inthe screen in said first wavelength region areobservable through said end of said envelope; means including a sourceof cath-' oderays mounted within said envelope at a 'position remotefrom said screen fordirecting a beam of cathode rays at said screenandfor causing said beam to scan said screen; an electrostatic shieldwithin said envelope encircling the region between said cathode raysource and said screen, said shield having a window formed therein;

'and a source for emitting radiation in said second wavelength regionpositioned to radiate through said window onto said screen.

28. In a cathode ray tube comprising a tubular mem her having anenlargedface at one end and a small shank at the other end, said faceand said shank being connected by a wall member; a coating of conductivematerial applied to the interior of said wall member from a pointadjacent said face to a point adjacent said shank, said coating formingan electrostatic shield, said coating having a said cylindrical headhaving a face thereon, a ring of con-1 ductive material coated on theinterior of the cylindrical portion of said tubular member and a ring ofconductive material coated on the interior of the conical portion,leaving a transparent window in said step; a luminescent screen withinsaid tubular member adjacent said face, the material. forming saidscreen having a characteristic that is altered in a first wavelengthregion whenexcited by cathode rays and that is restored upon exposure toradiation in a second wavelength region, said face being transparent insaid first wavelength region whereby alterations in the screen in saidfirst wavelength region are observable through said face; meansincluding a source of cath-.

ode rays mounted within said shank for directing 2 beam of cathode raysat said screen and for causing sa' bean: to scan said screen; and anelongated source for emitting radiation in said second wavelengthregion-encircling said transparent window between the ends thereof, aluminescent screen mounted on said face, said screen having acharacteristic that is altered in a first wavelength region when excitedby cathode rays and that is restored upon exposure to radiation in asecond wavelength region, said face being transparent in said firstwavelength region whereby alterations in the screen in said firstwavelength region are observable through said face; means including asource of cathode rays mounted within said shank for directing a beam ofcathode rays atsaid screen and for causing said beam to scan saidscreen; and a source for emitting radiation in said second wavelengthregion positioned to radiate through said window onto said screen.

29. In a cathode ray tube comprising a tubular member having an enlargedcylindrical head at one end and a small shank at the other end, saidcylindrical head being connected to said shank by a conical neck and astep, said i cylindrical head having a face thereon, a luminescent ofcathode rays at said screen and for causing said beam toscan saidscreen; and an elongated source for emitting tubular member behind saidstep for projecting radiation through said window onto said screen.

31. In a cathode ray tube, a transparent plate, a cascade screen on therear side of said plate and comprising a front layer and a back layer,said'front layer being characterized by emitting radiation in a firstwavelength region when excited by radiation in a second wavelengthregion and by becoming deexcited upon exposure to radiation in athirdwavelength region, wavelengths in said second region being shortcompared with wavelengths in said first region and wavelengths in saidthird region'beinglong compared with wavelengths in said first: region,said back layer being characterized by emitting radiation in said secondwavelength region when excited by cathode rays;

a source of cathode rays for exciting said screem'and a length regionmounted behind'said-screem' separate source for. emitting radiationinsaid third wave- 32. In a cathode rayhtu esscreemfflatransparent-plate, a luminescent screen the rear "side {of1-,;sstapmsma; characterized by emitting radiation in at'ljtstwavelengthregion when excited by cathod e rays-and by'becomitigdeexcited upon exposure to radiation in; asecon'dwavelen'gthi;

seeondwavelength region beregion, wavelengths in said ing longcomparedwith wavel engths'in aid first wave 1' length region, and afilter on same-side of said screen: as said transparent platecharacterized;by transaiitting" radiation in said first wavelengthregion therethrough and-f. preventing radiation in saidsecondwavelength-region) from-being transmitted therethrough.

33. In a cathode ray tube having an envelope a luminescent screenmounted within said envelope adjacent. one end of said envelope, thematerial forming said screen having a characteristic that is visiblyaltered inafirst wavelength region when excited by' cathoderays and thatis restored upon exposure to radiation in a second-wavelength region,said end of said envelope being-transparent in said first wavelengthregion whereby alterations in the screen in said first wavelength regionare visible through said end of said envelope; means including a sourceof cathode rays mounted within said envelope for directing a beam ofcathode rays at said screen and for'ca'using said beam to scan saidscreen; and a source for emitting radiation in said second wavelengthregion mounted between said screen and said cathode ray source.

References Cited in the file ofthis patent UNITED STATES PATENTS2,124,225 Batchelor "i July 19, 1938 2,247,112 Batchelor June 24, 1941(Other references on following page) 30. In acathode ray tube comprisinga tubular "ntemhaving an enlarged cylindrical head at one end and asmall shank at the other end, said cylindrical head being Aronstcin Feb.8, 1949 Buaigniea May 31, 1949 Rosenthal Sept. 13, 1949 Swcdlund Maylfi,1950 Blout Oct. 10, 1950 Cage May 15, 1951 Leverenz Aug. 7, 1951

